Merge pull request #1728 from flouc001/nfe/dry-run-slug

NFE: add dry run capabilities to default slugger

docs/USING_PRO.md

@@ -82,6 +82,18 @@ slugger.slug('foo-1') // foo-1-2
 ...
 ```
 
+`slugger.slug` can also be called with the `dryrun` option for stateless operation:
+```js
+slugger.slug('foo')                    // foo
+slugger.slug('foo')                    // foo-1
+slugger.slug('foo')                    // foo-2
+slugger.slug('foo', { dryrun: true })  // foo-3
+slugger.slug('foo', { dryrun: true })  // foo-3
+slugger.slug('foo')                    // foo-3
+slugger.slug('foo')                    // foo-4
+...
+```
+
 `flags` has the following properties:
 
 ```js

src/Slugger.js

@@ -6,28 +6,44 @@ module.exports = class Slugger {
     this.seen = {};
   }
 
-  /**
-   * Convert string to unique id
-   */
-  slug(value) {
-    let slug = value
+  serialize(value) {
+    return value
       .toLowerCase()
       .trim()
       // remove html tags
       .replace(/<[!\/a-z].*?>/ig, '')
       // remove unwanted chars
       .replace(/[\u2000-\u206F\u2E00-\u2E7F\\'!"#$%&()*+,./:;<=>?@[\]^`{|}~]/g, '')
       .replace(/\s/g, '-');
+  }
 
+  /**
+   * Finds the next safe (unique) slug to use
+   */
+  getNextSafeSlug(originalSlug, isDryRun) {
+    let slug = originalSlug;
+    let occurenceAccumulator = 0;
     if (this.seen.hasOwnProperty(slug)) {
-      const originalSlug = slug;
+      occurenceAccumulator = this.seen[originalSlug];
       do {
-        this.seen[originalSlug]++;
-        slug = originalSlug + '-' + this.seen[originalSlug];
+        occurenceAccumulator++;
+        slug = originalSlug + '-' + occurenceAccumulator;
       } while (this.seen.hasOwnProperty(slug));
     }
-    this.seen[slug] = 0;
-
+    if (!isDryRun) {
+      this.seen[originalSlug] = occurenceAccumulator;
+      this.seen[slug] = 0;
+    }
     return slug;
   }
+
+  /**
+   * Convert string to unique id
+   * @param {object} options
+   * @param {boolean} options.dryrun Generates the next unique slug without updating the internal accumulator.
+   */
+  slug(value, options = {}) {
+    const slug = this.serialize(value);
+    return this.getNextSafeSlug(slug, options.dryrun);
+  }
 };

test/unit/marked-spec.js

@@ -63,6 +63,29 @@ describe('Test slugger functionality', () => {
     const slugger = new marked.Slugger();
     expect(slugger.slug('<em>html</em>')).toBe('html');
   });
+
+  it('should not increment seen when using dryrun option', () => {
+    const slugger = new marked.Slugger();
+    expect(slugger.slug('<h1>This Section</h1>', { dryrun: true })).toBe('this-section');
+    expect(slugger.slug('<h1>This Section</h1>')).toBe('this-section');
+  });
+
+  it('should still return the next unique id when using dryrun', () => {
+    const slugger = new marked.Slugger();
+    expect(slugger.slug('<h1>This Section</h1>')).toBe('this-section');
+    expect(slugger.slug('<h1>This Section</h1>', { dryrun: true })).toBe('this-section-1');
+  });
+
+  it('should be repeatable in a sequence', () => {
+    const slugger = new marked.Slugger();
+    expect(slugger.slug('foo')).toBe('foo');
+    expect(slugger.slug('foo')).toBe('foo-1');
+    expect(slugger.slug('foo')).toBe('foo-2');
+    expect(slugger.slug('foo', { dryrun: true })).toBe('foo-3');
+    expect(slugger.slug('foo', { dryrun: true })).toBe('foo-3');
+    expect(slugger.slug('foo')).toBe('foo-3');
+    expect(slugger.slug('foo')).toBe('foo-4');
+  });
 });
 
 describe('Test paragraph token type', () => {